Data in a distributed database system is stored across a multitude of physically and/or logically distinct hosts. For example, data in a distributed database system may be stored on different host computers. Alternately or additionally, data in a distributed database system may be managed by separate host processes. To fulfill a query in a distributed database system, a query processing engine may generate an execution plan setting forth the data processing operations (e.g., join, aggregation, filter, relation) required by the query. The query processing engine may further distribute portions of the execution plan to the appropriate hosts, thereby delegating the data processing operations to the hosts storing and/or managing the relevant data.